This invention relates to an artificial kidney device and in particular an artificial kidney device provided with a liquid pressure adjusting means for automatically maintaining an ultrafiltration pressure substantially constant and a safety means for preventing inflow of an excessive amount of gas to a human vein.
By "an ultrafiltration pressure" is meant a difference between internal and external pressures applied to a dialysis membrane consisting of a semipermeable membrane which is provided within a dialyzer.
A variety of artificial kidney devices, for example, a coil type, a keel type or a type utilizing hollow fibers has been known up to this date. These artificial kidney devices are adapted to send blood from the artery of human being through a suitable means to a dialyzer where urea, nitrogen, sodium, potassium, water content etc., included in blood are separated through a semipermeable membrane. The blood passed through the dialyzer is returned to the vein of the human being. With the dialyzer, the water content should be eliminated, in an amount far greater than that of the other components, through the semipermeable membrane. In addition to osmotic pressure, therefore, an additional pressure is generally required for the dialysis operation. One method is to apply ultrafiltration pressure to a dialyzer in an attempt to eliminate more water content. Taking the strength etc. of the semipermeable membrane into consideration, the ultrafiltration pressure is generally desired to be maintained at a level of 200 mm Hg. If the ultrafiltration pressure is too high, there is a fear that blood will flow out due to a breakage of the semipermeable membrane. If, on the other hand, it is too low, a dialyzing effect is lowered, and water content is not sufficiently eliminated from blood. For the purpose of maintaining the ultrafiltration pressure at suitable level, a method employed in a prior art positive pressure type artificial kidney device is to transport a pressurized blood from artery to a dialyzer by a pumping means and to mount a pinch-cock midway of a tube extending from a dialyzer into a vein of a human being. An ultrafiltration pressure can be provided by restricting the flow passage of the tube by means of the pinch-cock.
However, a very delicate operation of the pinch-cock is required in adjusting the ultrafiltration pressure. Any slight operation of the pinch-cock causes a greater change in the resistance of blood. To make the ultrafiltration pressure at a prescribed level, therefore, the adjustment of the pinch-cock is conducted gradually, i.e. by repeating the adjustment several times. It will take more than two minutes for ultrafiltration pressure to settle down to a prescribed level after one adjustment has been made. For this reason, more than ten minutes will be required in adjusting the ultrafiltration pressure to a desired level. If no due care should be exercised during adjustment, there is a chance that blood will flow out due to a breakage of the dialysis membrane.
The ultrafiltration pressure is related not only to the extent to which the pinch-cock is closed but also to the operation of means for transporting blood from the artery of a human being into a dialyzer, for example, rotations of a pump. If, therefore, the pump is changed in the number of rotations to increase a flow of blood, the above-mentioned delicate adjustment will be required on each occasion.
As a settlement to the above-mentioned problems, we proposed in U.S. patent application Ser. No. 529,500 an artificial kidney device equipped with pressure adjusting means for automatically maintaining at all times constant the ultrafiltration pressure of a dialyzer in spite of a change in an amount of blood, for example, a change of blood pressure or a change in the number of rotations of a pressure pump for blood.
FIG. 1 is a schematic diagram showing an artificial kidney device proposed in the above-mentioned U.S. Patent Application and also applicable to this invention which is provided with a coil type dialyzer. A tube 1 is connected at one end to the artery of a human being and at the other end to the dialyzer 2. Midway of the tube 1 is connected a pump 3 for sending blood to the dialyzer 2 at a predetermined flow rate. The dialyzer 2 is a known coil type formed by winding one or a plurality of semipermeable membranes, into a coil 4 with a mesh interposed therebetween and submerging the coil into a dialysis solution 6 within a container 5. The dialysis solution 6 from the mixer 7 is supplied to and discharged from an outlet 8 while it is contacted with a dialysis membrane.
On the other hand, blood is passed through the dialyzer 2, where unnecessary components are separated, and flows through a tube 9 into the vein of the human being. Midway of the tube 9, a drip tube 11 connected to a manometer 10 and a double-walled tube 12 connected to an air pump 13 and air reservoir 14 are provided in communication with the tube 9. FIG. 2 shows the details of the drip tube 11, the air pump 13, the air reservoir 14 and the double-walled tube 12. As shown in FIG. 2 the blood passed through the dialyzer 2 is sent through the tube 9 to the drip tube 11 and then flows through a mesh 15 into the double-walled tube 12. The double-walled tube 12 has an inner tube 16 as shown in FIGS. 3 to 6 and an outer tube 17. The inner tube 16 is made of a material which allows opening or closing of the tube 16 due to a slight difference in pressure occurring between the inside and outside of the inner tube 16. As shown in FIGS. 4 and 6, the inner tube 16 is formed by superposing one over the other two sheets of non-rigid polyvinyl chloride and sealing them at the side edge portions. The inner and outer tubes 16 and 17 of the double-walled tube 12 are hermetically heat sealed at each end to define a closed chamber 18 between the inner and outer tubes 16 and 17. The tube 19 is opened at one end into the closed chamber 18 and at the other end detachably connected to an air reservoir 20. A manually operated air pump 23 is connected through a tube 22 to the air reservoir 20 and adopted to adjust the air pressure prevailing within the air reservoir 20. 21 denotes a manometer for indicating an air pressure within the air reservoir 20. 24 and 25 denote valve means, respectively.
An explanation will now be made as to how an ultrafiltration pressure is automatically controlled in the so constructed artificial kidney device.
Blood from the artery of a human being is sent to the dialyzer 2. The air pump 23 is repeatedly squeezed for increasing pressure within the air reservoir 20 and closed chamber 18 so that a pressure prevailing within the dialysis coil of the dialyzer 2 comes to, for example, 200 mm Hg.
When the pressure within the dialysis coil 4 reaches 200 mm Hg, the valve 25 is closed and internal pressure in the inner tube 16 and closed chamber 18 takes an equilibrium state and the inner tube 16 is inflated to a suitable extent shown, for example, in FIGS. 4 and 6. When, however, the pressure within the dialysis coil 4 comes to below 200 mm Hg, the inner tube 16 of the double-walled tube 12 is collapsed as shown in FIGS. 5 and 7 with its opening being narrowed in cross section, since the internal pressure of the inner tube 16 is smaller than the external pressure of the inner tube 16. As the inner tube 16 is so collapsed, the blood passed through the dialysis coil is restricted, causing the ultrafiltration pressure to be recovered to a pressure of 200 mm Hg. In this way, the ultrafiltration pressure is automatically adjusted to 200 mm Hg. When, on the other hand, the pressure within the dialysis coil 4 exceeds 200 mm Hg, the internal pressure of the inner tube 16 exceeds the external pressure of the inner tube 16 causing the inner tube 16 to be again inflated as shown in FIGS. 4 and 6. As a result, blood flow rate is increased and the pressure prevailing within the dialysis coil is dropped and automatically adjusted to 200 mm Hg. In this way, the ultrafiltration pressure i.e. the pressure within the dialysis coil is automatically maintained to 200 mm Hg. This automatic adjustment is effected within several seconds to scores of seconds. In an automatic ultrafiltration pressure adjustment, the air reservoir 20 works as a pressure change absorbing means. A volume within the closed chamber 18 is somewhat changed due to the collapse or inflation of the inner tube 16. This change, however, is absorbed by a relatively great amount of air confined within the air reservoir 20. Consequently, the change of pressure within the closed chamber 18 due to the collapse or inflation of the inner tube 16 can be disregarded. From this viewpoint the greater the volume of the air reservoir 20, the better. The air reservoir 20 is, as above-explained, effective in an automatic adjustment of an ultrafiltration pressure. There is, however, a fear that if by any chance the inner tube 16 should be broken, a greater amount of air flows into the blood vessel of the human being. In this sense, the presence of the air reservoir 20 may also be considered as dangerous.
There are opinions in medical field that a volume of more than 20 cc of air entering into human vein would affect the health of human being in some way. Taking such a view into consideration it is advisable to prevent air from entering into human vein if by any chance.